1. Field of the Invention
The invention relates to electronic power supplies and power converters.
2. Description of the Related Art
Wiring in homes and other buildings has evolved over time to conform to fairly uniform standards. When a consumer in North America purchases an electrically-powered product, he generally does so without concern over its ability to use the electricity supplied by wiring in his house or office. The motors and bulbs in kitchen appliances, office equipment, lamps, power tools, and other electric devices are generally designed to be powered by a 120V AC supply (i.e.: a supply that delivers alternating current at 60 Hz with a potential of 120 volts RMS). The plugs for these devices and the sockets for the wiring outlets are also standardized. The standardization of these physical features ensures compatibility between the electric power supplies and the devices that use them. Other standards, such as the 220V AC system, similarly facilitate the design and use of electrical appliances in other regions of the world.
Many electronic devices, however, require a lower-voltage power source, and direct current instead of AC. To use the available electric power, such as 120V AC, these devices generally use a converter that transforms the available electric power to a lower voltage, rectifies it, and filters it to generate a constant-voltage (DC) supply. The output of the converter is DC at a low voltage, generally between 4 and 30 volts.
The converter may be incorporated into the device as an internal power supply that receives 120V AC through an electric cord that plugs into a wall socket. Alternatively, the converter may be an external unit, configured as a large wall plug for the device. An external converter generally plugs into a wall socket and supplies low-voltage DC electricity through a power cord. On the other end, the power cord either connects directly to the electronic device or has a plug configured for a socket in the electronic device.
A device that uses an external converter has the advantage of being somewhat lighter and more compact, since the additional circuitry and components do not have to be incorporated in the device. Thus, the external converters are commonly used with smaller household items such as answering machines, telephones, arid calculators, among others.
However, the external converters often become separated from their associated devices when equipment is moved from one room to another or from one building to another, or when equipment is placed in temporary storage. Further, both internal and external converters add a degree of complexity and expense to the electronic device. And in the case of custom-made electronic devices assembled by an electronics hobbyist, the hobbyist must either purchase or build a power supply to test and operate her custom device. It would therefore be convenient and economically beneficial to reduce the reliance on dedicated AC/DC converters for individual electronic devices.